Paper and paper-like materials having a remoistenable adhesive coating



United States Patent Ofiice PAPER AND PAPER-LIKE MATERIALS HAVING AREMOISTENABLE ADHESIVE COATING Harry A. Toulmin, Jr., Dayton, Ohio,assignor to The Commonwealth Engineering Company of Ohio, Dayton, Ohio,a corporation of Ohio No Drawing. Application November 27, 1953, SerialNo. 394,884

8 Claims. (Cl. 117-122) This invention relates to novel pregummedpapers, and is more particularly concerned with pre-gummed papers whichmay be remoistened to develop latent adhesive properties.

Although, as will be understood, the invention is not limited thereto,it will be discussed in detail in connection with pre-gurnmed hangingpapers having satisfactory slip characteristics and which, onremoistening, develop latent adhesive and bonding properties, that ishanging papers one side of which carries a coating of adhesive materialthat is normally substantially non-adhesive but that, on moistening withplain water or aqueous media, becomes adhesive permitting bonding of thepaper to other materials such as plaster. Paper or paper articlescarrying the potentially adhesive coating or film may be classified aspre-gummed articles, or pre-gummed paper. Wallpaper, poster paper,sealing paper and the like may be described as pre-gummed paper.

The provision of an acceptable pre-gummed hanging paper presents manydilficulties. Such papers would be of particular value for amateur usein the home because the average person is unskilled in hanging paper andis generally not successful in using wallpaper and the like as presentlymarketed, i. e., without a potentially adhesive coating and requiringthe application of an adhesive to it immediately prior to use.

It is known that, to be acceptable, pre-gummed hanging paper must haveboth good slip characteristics and the capacity to bond strongly to thesurface to which it is applied. While becoming adhesive whenremoistened, it must also be sufiiciently resistant to atmosphericmoisture to remain substantially dry and non-tacky until actually wetwith moisture, so that the paper can be rolled up on itself and drawnoff from the roll as needed. Once moistened to develop the latestadhesiveness, the paper must be capable of being slipped on a wall whilein the remoistened condition so that, in hanging wallpaper for example,the person hanging the paper in the usual way, that is in the form ofstrips, can slip the newly added strip relatively of others, already inplace, before it sets in the bonded condition, for accurate matching ofpatterns. In addition, after the latent adhesiveness is developed bywetting and the paper is hung and dried in place on a wall or the like,the bond should not be susceptible to loosening by the action ofatmospheric moisture on the adhesive. A wholly satisfactory pre-gummedhanging paper having all of these properties and characteristics andmeeting all of these requirements, and having the important advantage oflow cost, has not been available heretofore. 7

One object of this invention is to provide novel, improved pre-gummedpaper carrying a potentially adhesive relatively low-cost coating havingthe properties and characteristics set forth above and which satisfiesthe requirements for a commercially acceptable paper of this type.

Other objects and advantages of the invention will appear hereinafter.

2,768,096 Patented Oct. 23, 195

The objects of the invention are achieved by providing paper, forinstance, hanging paper, with a coating of dextran or a dextranconversion product that, on remoistening, becomes adhesive and on dryingin place on an appropriate surface, such as a wall, becomes and, undernormal conditions remains, tightly bonded thereto.

The dextrans are high molecular Weight polysaccharides made up ofanhydroglucopyranosidic units and characterized in that the linkagesbetween the units are of both alpha-1,6 and non-aIpha-1,6 type, at least50% of these linkages being, apparently, of the alpha-1,6 type.

A. striking feature of the deXtrans is the wide variations they exhibitwith respect to their physical and structural properties includingmolecular weight, molecular structural repeating alpha-1,6 tonon-alpha-1,6 linkages ratios, and water-sensitivity. As to the latterproperty, while the so-called native dextrans, being hydroxylbearingsubstances, are hydrophilic, some of the dextrans are readily soluble inwater whereas others are difiicultly soluble in water, are initiallyswollen thereby and only ultimately, if at all, completely dissolvedtherein.

A Wide variety of dextrans may be used in practicing this inventionwhich, as stated above, is not limited to the provision of hangingpapers. The dextran used as latent or potential adhesive may have amolecular weight of 5000 to x10 as determined by light scatteringmeasurements, a molecular structural repeating alphal,6 to non-alpha-l,6linkages ratio of 1.9:1 to 30:1 and be soluble or substantiallyinsoluble in water, depending on the use for which the pre-gummed paperproduct or article is intended.

The dextrans may be obtained by various methods. They may be synthesizedfrom sucrose by enzyme action in the presence or substantial absence ofbacteria. For example, an aqueous nutrient medium containing sucrose,particularly nitrogenous compounds and certain inorganic salts, may beinoculated with a culture of an appropriate microorganism such as thoseof the Leuconostoc meseitteroides and L. dextram'cum types, andincubated at the temperature most favorable to the growth of themicroorganism until maximum dextran production is attained. This issynthesis of the dextran from sucrose by the so-called whole culturemethod, i. e., the synthesis is effected by enzyme action in thepresence of the bacteria and cellular debris. Or the culture obtained bycultivating the Leuconostoc bacterium may be filtered to isolate theenzyme (dextransucrase) which occurs in the filtrate, the filtrate,usually after dilution to predetermined enzyme potency, may be mixedwith an aqueous sucrose solution, and the mixture may be allowed tostand under controlled conditions of pH and temperature until thedextran is synthesized. The enzyme may be separated from the filtrateand used in powdered condition or in the form of an aqueous solution,usually the latter. This is dextran synthesis by enzyme action in thesubstantial absence of bacteria and cellular debris.

The dextran obtained initially by these procedures is so-called nativedextran which normally has a very high average molecular weight,calculated to be in the millions. It may be precipitated from the mediumin which it is synthesized by the addition of an organic liquid which isa non-solvent for the dextran. The nonsolvent, or precipitant, may be aWater-miscible aliphatic alcohol, e. g., methanol, ethanol orisopropanol, or a ketone such as acetone or dioxane. The precipitateddextran may be purified and dried to a substantially white mass whichmay be reduced to powdered condition for use in preparing the presentadhesive composition.

Native or high molecular weight dextran may be hydrolyzed under acid orneutral conditions, or by enzyme action to a molecular weight lower thanthat of the native material. Thus clinica dextran has an averagemolecular weight of from 20,000 to 200,000. In clinical dextranproduction, when the desired molecular weight is obtained by hydrolysisor cleavage of the native material, it is usual to isolate the clinicalproduct from the hydnolyzate by fractional precipitation according towhich, by successive addition of increasing amounts of watermisciblealcohol or ketone, the highest molecular weight fraction is first throwndown and separated, and the desired or intermediate molecular fractionis then precipitated and recovered. This procedure leaves a supernatantcontaining dextran the average molecular weight of which is below theclinical range, and the supernatant is usually discarded as waste. Thedifferent dextran fractions may also be isolated from the hydrolyzate byfractional solution methods involving the use of the precipitant inconjunction with a dextran solvent, usually water. It may be noted,here, that when the dextran synthesis is effected by the action of theenzyme on sucrose in the absence of bacteria, it is possible to carryout the synthesis under conditions such as to favor the production ofdextran of relatively low molecular weight in at least preponderantproportion. It is possible, therefore, as is now known, to obtainrelatively low average molecular weight dextran by direct enzymaticsynthesis from sucrose.

When dextran is synthesized from sucrose by enzyme action, in thepresence or substantial absence of bacteria and cellular debris, thewater-sensitivity of the native dextran obtained is influenced by themicroorganism cultivated to obtain the culture, or enzyme isolatabletherefrom, introduced into the sucrose-bearing medium in which thedextran is to be synthesized. Thus, native dextrans synthesized by theuse of the microorganisms bearingthe following NRRL (Northern RegionalResearch Laboratories) classifications, or their enzymes, are quitereadily soluble in Water: Leuconostoc mesenteroides 13-512, 13-1146,13-119, and B-1196. These dextrans are, usually, smooth, lustrous,elastic gums which are quite readily soluble in water to give clear orsubstantially clear solutions.

The native dextrans from the microorganisms (or their enzymes) (NRRL)Leuconostoc mesenteroides B-742, 13-1191, B-l196, B1208, and 13-1216,and from Streptobacterium dextranicum 15-1254 are, generally speaking,rather rough, dull, non-elastic gums which may be regarded as relativelyinsoluble in water but which are water-swellable and go into solution inwater under heating and stirring to give viscous solutions that aresomewhat turgid.

A third group of native dextrans is represented by and includes thoseobtained from microorganisms (or their enzymes) bearing the NRRLclassifications: Leuconostoc mesenteroides Bl120, B-ll44, 13-523, andBetabacterium vermiforme Bll39. T hese dextrans are generally more orless flocculent gums which are swellable by water but which are, for allpractical purposes, substantially insoluble therein.

The adhesive composition may be prepared by mixing a sufiicientproportion of the selected dextran, preferably high molecular weight ornative dextran, with water or an organic solvent which at least swellsor partially solvates the dextran, to obtain a thick, viscous,non-running solution or soft paste which can be applied to the surfaceof a paper sheet, strip or preformed article in any conventional manner,as by brushing or by roller application.

Water-soluble dextrans may be used and may be applied in the form ofthick, viscous, non-running aqueous solutions. Or, and often preferably,the difficultly watersoluble to substantially water-insoluble dextransmay be used. These may be mixed with water to a soft paste, if desiredin the presence of suitable dispersing agents such as the commerciallyavailable Tweens and Spans (partial higher-fatty acid esters ofpolyhydric alcohols of the type of sorbitan mono-stearate andpolyoxylethylene condensates of the polyhydric alcohol esters) or theymay be mixed with solvents therefor to obtain soft workable pastescapable of being brushed on the paper. For example, the water-insolubledextrans are soluble in aqueous alkaline solution, such as aqueoussodium hydroxide, and in such solvents'as morpholine, acylamides such asformamide and the lower monoand di-acylamides such as monoand di-methylformamide, and these solvents may be used in making the viscousnon-running solutions or pastes.

After the coating is applied to the paper and dried, the coated surfaceis substantially non-tacky. However, when the paper is to be used,remoistening of the coating with a controlled amount of water orswellant or a limited amount of solvent sufficient to effect a partialsolvation of the dextran, will render the latter adhesive so that it canbe bonded, with moderate pressure, to the surface to be decorated and/or protected.

The paste can be prepared at room temperature or under heating totemperatures of 50 C. to C., with continued stirring until the mass issubstantially homogeneous.

Being inherently hydrophilic, the dextrans have the advantage that whenit is desired to remove wallpaper or the like bonded to the wall bydextran, the paper can be readily stripped off by moistening or wettingit with water whereby the dextran is swollen and the bond between it andthe surface loosened to permit easy peeling of the paper.

The following examples, in which the parts are by weight, are given toillustrate specific embodiments of the invention, and it is to beunderstood that these examples are not intended to be limitative.

Example I About 30 parts of particulate native L. m. B-5l2 dextran aremixed with 70 parts of water at room temperature to obtain a soft paste.This paste is applied evenly and uniformly over a surface of a wallpaperraw stock, and dried to obtain a finished pre-gummed wallpaper whichrequires only moistening of the coated surface before being hung andbonded to the wall. It can he slipped, while the coating is in the moiststate, on the wall surface for matching the pattern and on drying isfirmly bonded to the wall without the persistence of bulges or blistersformed in the paper while the dextran coating is still in the moist,tacky condition.

Example 11 7 About 25 parts of particulate native L. m. B-523 dextranare mixed with parts of water at about 60 C. whereby the normallysubstantially water-insoluble dextran is swollen and forms a viscousmass or soft paste which is non-running but has sufficient fluidity foreasy application by brushing. The paste is applied as an even, uniformcoating to a surface of wallpaper raw stock, and dried. On remoisteningwith water, the dextran is again swollen and becomes adhesive. While thecoating is in the remoistened condition, the paper can be hung, slid onthe wall surface as required, and then allowed to dry thereon. It isadhesively bonded to the wall.

The pre-gummed papers carrying the dextran coating have a significantcost advantage over previously proposed pre-gurnmed papers. Whereasother gums have been chemically modified or pre-treated to render themsuitable for this purpose, and the chemical modification necessarilyadds to the cost of the adhesive and of the final coated paper, the highmolecular weight dextrans such as the native dextrans obtained byenzymatic synthesis from sucrose may be used directly for preparing thepastes and are generally preferred.

Auxiliary agents may be mixed with the dry base adhesive comprisingdextran, for special purposes, or such materials may be incorporated inthe liquid used to remoisten the dextran coating. For instance, it maybe desirable to disperse or dissolve in the adhesive or potentiallyadhesive base, or in the moistening liquid, plasticizing agents, orauxiliary agents which favorably influence the adhesive characteristicsof the base. Illustratively, when the dextran paste, viscous solution ordispersion, is to be used in preparing pre-gummed hanging papers it maybe desirable to include, as plasticizing agents, such normally solidmaterials as urea, thiourea, sodium nitrate, sodium thiocyanate,potassium thiocyanate, potassium nitrate, calcium chloride, magnesiumchloride, and zinc chloride. Or plasticizing liquids of the type ofglycerine, diethylene glycol, ethylene glycol, sodium lactate and othersmay be used. Additional plasticizers include sodium acetate, sodiumchloride, sodium diacetate, sodium monophosphate, ammonium chloride andsugars. Viscosity increasing agents such as borax and sodium aluminatemay also be included in the paste or soft, viscous solution ordispersion, as Well as various wetting agents, solvents and fillingmaterials, to attain the special eifects or results for which it isconventional in the art to use those adjuvants. Small amounts of oil,grease of wax may be worked into the adhesive base.

When any of the foregoing or equivalent auxiliary agents are used, theamount thereof may vary but will usually be small, and not more thanabout 5% of the total solids content of the composition. If oil, greaseor wax is used, proportions of 0.5% to 3.0% of the solids content willusually be satisfactory. The amount of any auxiliary substance usedshould be controlled and such that the coated surface of the base, afterdrying thereof, is in non-tacky condition.

Although the invention has been described in terms of hanging paper suchas Wallpaper and poster paper, it will be evident that the invention isnot limited thereto.

The adhesive dextran composition having remoistening characteristics maybe applied to paper to be used for a variety of purposes. It may beapplied to paper in strip form to be used for sealing paper containersand paper wrappings. The compositions, especially those in whichnon-aqueous liquids are used in the preparation thereof and forremoistening the coating, may be applied to paper-like products such astransparent sheeting, film or strip, e. g., of regenerated cellulose, toobtain products to be adhesively bonded to a base and includingnonfibrous sealing tapes. It will be evident also that various paperarticles, such as envelopes, stamps, Christmas and other types ofpackage seals, mailing labels, etc. may be provided with a dextrancoating to be rendered adhesive on remoistening. As is known, some ofthese articles are often remoistened by licking with the tongue. Nounpleasant taste or other harm can ensue if this is done to an envelope,stamp or the like the adhesive coating of V which comprises dextran. Thedextrans are bland, tasteless, odorless, non-toxic and non-irritatingsubstances which are physiologically harmless and, in fact, edible.

The dextran-containing coating composition may comprise pigments, forinstance mineral pigments such as china clay, calcium carbonate, satinwhite and the like, for specific purposes or uses of the composition.

Since numerous changes and modifications may be made in the detailsgiven, in practicing the invention, without departing from its spiritand scope, it will be understood that it is not intended to limit theinvention except as defined in the appended claims.

What is claimed is:

1. Pre-gummed paper-like sheet material having a normally substantiallynon-tacky but potentially adhesive by moistening coating consistingessentially of dextran.

2. A pre-gummed hanging paper having a normally substantially non-tackybut potentially adhesive by moistening coating consisting essentially ofdextran.

3. Pre-gummed wallpaper having a normally substantially non-tacky butpotentially adhesive by moistening coating consisting essentially ofdextran.

4. A pre-gummed paper product having a coating consisting essentially ofa ditficultly water-soluble to substantially Water-insoluble butWater-swellable dextran, said coating being normally substantiallynon-tacky and rendered adhesive by moistening with aqueous media toswell the dextran.

5. A pre-gummed hanging paper having a coating consisting essentially ofa ditficultly. water-soluble to substantially water-insoluble dextran,said coating being norm-ally substantially non-tacky and renderedadhesive by moistening with aqueous media to swell the dextran.

6. Pre-gummed wallpaper having a coating consisting essentially of adiliicultly water-soluble to substantially Water-insoluble dextran, saidcoating being normally substantially non-tacky and rendered adhesive bymoistening with aqueous media to swell the dextran.

7. Strip sealing paper-like sheet material having a normallysubstantially non-tacky but potentially adhesive by moistening coatingconsisting essentially of dextran.

8. Strip sealing paper-like sheet material having a coating consistingessentially of a diflicultly water-soluble to substantiallywater-insoluble but water-swellable dextran, said coating being normallysubstantially non-tacky and rendered adhesive by moistening to swell thedextran.

References Cited in the file of this patent UNITED STATES PATENTS2,183,736 Bauer Dec. 19, 1939 2,288,527 Humphner June 30, 1942 2,503,624Luaces Apr. 11, 1950 2,674,584 Deniston Apr. 6, 1954

1. PRE-GUMMED PAPER-LIKE SHEET MATERIAL HAVING A NORMALLY SUBSTANTIALLYNON-TACKY BUT POTENTIALLY ADHESIVE BY MOISTENING COATING CONSISTINGESSENTIALLY OF DEXTRAN.